COMPLEX

The function complex takes two rational number arguments and
returns an ACL2 number. This number will be of type
(complex rational) [as defined in the Common Lisp language], except
that if the second argument is zero, then complex returns its first
argument. The function complex-rationalp is a recognizer for
complex rational numbers, i.e. for ACL2 numbers that are not
rational numbers.

The reader macro #C (which is the same as #c) provides a convenient
way for typing in complex numbers. For explicit rational numbers x
and y, #C(x y) is read to the same value as (complex x y).